Agents that do not persist in a suspended state and sediment must be resuspended prior to use. One example of an agent that must be resuspended prior to use is a pharmaceutical colloid, such as a contrast agent that is injected into a patient to enhance an imaging procedure. Contrast agents are used in various types of imaging including x-ray, magnetic resonance imaging (MRI), computed tomography (CT) and ultrasound (US). A contrast agent that comes out of suspension must be resuspended before placing the desired volume to be dosed into a delivery container such as a syringe. If there is a delay before the dose is injected into a patient, for example while preparing the patient or equipment, or if the infusion is extended, the agent must again be suspended before or during administration.
Resuspension of contrast agent requires mechanical manipulations, for example, removing a filled syringe positioned in an injector and remixing its contents. Additional remixing steps may delay a critical infusion time or, if remixing is omitted, the entire imaging procedure may have to be repeated due to suboptimal contrast obtained. Duplicate procedures not only put patients at increased risk and inconvenience, but are also cost- and time-inefficient. Even if the need to resuspend a single bolus injection is not prohibitive for a given procedure, repeated bolus injections or long term continuous infusions can become problematic due to the agent coming out of suspension during administration.
The loss of suspension for a contrast agent at any point in a delivery system to a patient, such as in a syringe and/or in the connecting tubing, severely limits the duration of continuous infusions or the time between intermittent injections. The need to initially resuspend the colloid or other type of agent, and to further suspend if the agent is not used shortly after resuspension, requires either time-consuming effort and vigilance by the user or the use of mechanical mixing devices. In any case, the need to resuspend an agent poses an additional step and a possible source of error in an imaging procedure.